Let's look at a complete program to the understand use of these methods.

Consider the following input:

<n1=v1 n2=v2 n3=v3> n1=v1 n2=v2 abc=123 <v=pq id=abc> v=pq 

We need to write code to swap each name-value pair enclosed in angular brackets, < and >, while leaving the name-value pairs outside the angular brackets unchanged. After running our code, it should produce the following output:

<v1=n1 v2=n2 v3=n3> n1=v1 n2=v2 abc=123 <pq=v abc=id> v=pq 

To solve this problem, we have to first find each match enclosed in angular brackets using the find method in a loop. Inside the loop, we will have to replace each name-value pair using the appendReplacement method. Finally, outside the loop, we will use the appendTail method to append the remaining characters after our last match.

Here is the full code:

package example.regex; 

import java.util.regex.*; 

class MatcherAppendExample 
{ 
  public static void main (String[] args) 
  { 
    final String input = "<n1=v1 n2=v2 n3=v3> n1=v1 n2=v2 abc=
    123 <v=pq id=abc> v=pq"; 

    // pattern1 to find all matches between < and >  
    final Pattern pattern = Pattern.compile("<[^>]+>");  

    // pattern1 to find each name=value pair  
    final Pattern pairPattern = Pattern.compile("(\w+)=(\w+)");  

    Matcher enclosedPairs = pattern.matcher(input);  

    StringBuilder sbuf = new StringBuilder(); 

    // call find in a loop and call appendReplacement for each match  
    while (enclosedPairs.find())  
    { 
      Matcher pairMatcher = pairPattern.matcher(enclosedPairs.group());  
      // replace name=value with value=name in each match  
      enclosedPairs.appendReplacement(sbuf, 
      pairMatcher.replaceAll("$2=$1"));  
    } 

    // appendTail to append remaining character to buffer   
    enclosedPairs.appendTail(sbuf);  

    System.out.println(sbuf);  
  } 
} 

Upon compiling and running, the preceding code will produce the following output:

<v1=n1 v2=n2 v3=n3> n1=v1 n2=v2 abc=123 <pq=v abc=id> v=pq 

As you can see, the final output has all the name=value pairs swapped inside the angular brackets.